BOSTON -- NBA veteran center Jason Collins, the first active athlete in one of the four U.S. major professional sports leagues to come out as being gay, marched Saturday for nearly three miles in Boston's gay pride parade with U.S. Rep. Joe Kennedy III, his onetime roommate at Stanford University.

Collins wore a T-shirt that read (hash)BeTrue when he joined thousands of marchers in the parade, chatting with well-wishers, greeting other marchers and holding babies as people came up to him to express their support.

The parade also featured former U.S. Rep. Barney Frank - the first sitting member of Congress to enter into a same-sex marriage - who also represented Massachusetts' 4th Congressional District before Kennedy. U.S. Rep. Ed Markey, the Democratic U.S. Senate candidate seeking the seat once held by John Kerry, who stepped down to become secretary of state, also marched.

The parade's grand marshal, Boston Mayor Thomas Menino, did not march because he is recovering from prostate surgery. Still, he came out of the city-owned house to greet Collins, Kennedy and other marchers as they passed by.

In coming out as gay in April, Collins wrote in an article for Sports Illustrated that his decision to go public came when Kennedy marched in last year's parade and Collins didn't feel that he could join him.

He also said the Boston Marathon bombing reinforced the notion that things can change in an instant, so he might as well live truthfully.

Collins played for six teams in 12 seasons and becomes a free agent next month. The Celtics dealt him to the Washington Wizards in a midseason trade.

Collins also threw out the ceremonial first pitch at the Red Sox game Thursday.

Kennedy said in April that he's proud to call Collins a friend.

Collins said at the time he "endured years of misery and gone to enormous lengths to live a lie."